[0001] The present invention relates to an electrophoretic display device, a method of driving
the same, and an electronic apparatus.
[0002] An electrophoretic display device is capable of displaying an image by generating
a potential difference between pixel electrodes and a common electrode provided in
a pair of substrates interposing an electrophoretic element including a dispersion
medium containing electrophoretic particles and by moving the electrophoretic particles
(for example, see
JP-A-2002-116733,
JP-A-2003-140199,
JP-A-2004-004714, and
JP-A-2004-101746). In such an electrophoretic display device, scanning lines used to selectively drive
pixel electrodes, data lines, and pixel switching transistors are formed on a substrate
of the pair of substrates which is provided with pixel electrodes formed in pixels,
to perform active matrix driving (for example, see
JP-A-2002-116733,
JP-A-2004-004714, and
JP-A-2004-101746).
[0003] However, not all the electrophoretic particles behave in completely the same manner,
even when a predetermined potential difference is generated between the pixel electrodes
and the common electrode in a predetermined period such as one frame period or one
horizontal scanning period. Therefore, a problem occurs in that the electrophoretic
particles cannot be moved up to a desired location. Moreover, a problem occurs in
that the electrophoretic particles may sink or rise due to convection currents of
the dispersion medium or gravity action even once the electrophoretic particles are
moved to or reach the desired location. Therefore, an image to be displayed is not
clear, a residual image occurs, or irregularity in colors or brightness between pixels
occurs. That is, a technical problem occurs in that defects with a display may occur.
[0004] An advantage of some aspects of the invention is that it provides an electrophoretic
display device capable of displaying a high-quality image, a method of driving the
electrophoretic display device, and an electronic apparatus equipped with the electrophoretic
display device.
[0005] According to an aspect of the invention, there is provided an electrophoretic display
device including: a pair of first and second substrates; an electrophoretic element
which is interposed between the first and second substrates and includes a dispersion
medium containing electrophoretic particles; a plurality of pixel electrodes which
are formed on the first substrate; a common electrode which is formed opposite the
plurality of pixel electrodes on the second substrate; an image signal supply unit
which supplies an image signal having a first potential or a second potential lower
than the first potential to the plurality of pixel electrodes in accordance with image
data; and a common potential supply unit which supplies a common potential to the
common electrode. The image signal supply unit supplies the image signal to the plurality
of pixel electrodes in each of a predetermined number of frame periods in an image
signal supply period containing the predetermined number of frame periods in accordance
with the image data associated with the same frame image as the image data. In addition,
the common potential supply unit switches the common potential into a third potential
equal to or lower than the first potential and higher than the second potential and
a fourth potential lower than the third potential and equal to or higher than the
second potential, and supplies the switched potentials to the common electrode in
each of the frame periods in the image signal supply period.
[0006] In the electrophoretic display device according to the aspect of the invention, one
pair of the first substrate and the second substrate are disposed so as to be opposed
to each other with the electrophoretic element interposed therebetween. On a side
of the first substrate opposed to the second substrate, the plurality of pixel electrodes
are arranged in a matrix shape in correspondence to intersections of the data lines
and the scanning lines which intersect each other on the first substrate, for example.
On the first substrate, for example, the transistors as the pixel switching elements,
which are provided in the pixels provided with the plurality of pixel electrodes,
are capable of performing active matrix driving. On the other hand, on a side of the
second substrate opposed to the first substrate, the common electrode is provided
in a solid state, for example, so as to be opposed to the plurality of pixel electrodes.
The electrophoretic element includes the dispersion medium containing the electrophoretic
particles (for example, a plurality of white particles charged to a negative polarity
and a plurality of black particles charged to a positive polarity).
[0007] In operation of the electrophoretic display device according to the aspect of the
invention, an image is displayed on the display unit including the plurality of pixels
by applying voltage (that is, a potential difference) according to the image signal
to the electrophoretic element interposed between the pixel electrodes and the common
electrode. More specifically, on the basis of the voltage applied between the pixel
electrodes and the common electrode, one of each white particle charged to the negative
polarity and each black particle charged to the positive polarity is moved (that is,
migrated) toward the pixel electrode in the dispersion medium and the other thereof
is moved toward the common electrode in the dispersion medium. In this way, an image
is displayed on a side of the second substrate in which the common electrode is formed.
At this time, the image signal supply unit supplies the image signal having the first
potential or the second potential lower than the first potential in accordance with
image data to the pixel electrodes through the transistors as the pixel switching
elements selected (that is, turned ON) upon supplying the scanning signal through
the data lines and the scanning lines. On the other hand, the common potential supply
unit supplies the common potential to the common electrode.
[0008] In particular, the image signal supply unit supplies the image signal to the plurality
of pixel electrodes in accordance with the image data associated with the same frame
image as the image data in each of the predetermined number of frame periods in the
image signal supply period containing the predetermined number of frame periods. Moreover,
the common potential supply unit switches the common potential into the third potential
and the fourth potential lower than the third potential in each of the frame periods
in the image signal supply period and supplies the switched potentials to the common
electrode. Here, "the image signal supply period" refers to a period in which the
image signal according to the image data associated with a frame image, which is an
image for one screen to be displayed, is supplied to the pixel electrodes. For example,
the image signal supply period is set as a period of ten times of the frame period.
"The frame period" is a unit period in which the frame image is displayed and a vertical
scanning period (also referred to as one vertical period or one V period) which is
set in advance in order to select all the plurality of scanning lines in a predetermined
order, for example. The third potential is generally the same potential as the first
potential and the fourth potential is generally the same potential as the second potential.
[0009] In a first frame period in the image signal supply period containing the first frame
period, a second frame period, ..., and an n-th frame period (where n is a natural
number) in this order, the fourth potential (which is generally the same potential
as the second potential) as the common potential is supplied to the common electrode.
In addition, voltage is applied between the common electrode and the pixel electrodes
to which the image signal having the first potential is supplied, and voltage is not
applied between the common electrode and the pixel electrodes to which the image signal
having the second potential is supplied. In the second frame period followed after
the first frame period, the third potential (which is generally the same potential
as the first potential) as the common potential is supplied to the common electrode.
In addition, no voltage is applied between the common electrode and the pixel electrodes
to which the image signal having the first potential is supplied, and voltage is applied
between the common electrode and the pixel electrodes to which the image signal having
the second potential is supplied. In the third frame period followed after the second
frame period, like the first frame period, the fourth potential as the common potential
is supplied to the common electrode. In addition, voltage is applied between the common
electrode and the pixel electrodes to which the image signal having the first potential
is supplied, and no voltage is applied between the common electrode and the pixel
electrodes to which the image signal having the second potential is supplied. In the
fourth frame period followed after the third frame period, like the second frame period,
voltage is applied or not applied between the common electrode and the pixel electrodes.
In this way, in the odd-numbered frame period, the fourth potential as the common
potential is supplied to the common electrode. In addition, voltage is applied between
the common electrode and the pixel electrodes to which the image signal having the
first potential is supplied, and no voltage is applied between the common electrode
and the pixel electrodes to which the image signal having the second potential is
supplied. On the other hand, in the even-numbered frame period, the third potential
as the common potential is supplied to the common electrode. In addition, no voltage
is applied between the common electrode and the pixel electrodes to which the image
signal having the first potential is supplied, and voltage is applied between the
common electrode and the pixel electrodes to which the image signal having the second
potential is supplied.
[0010] That is, in each of the frame periods in the image signal supply period, the voltage
according to the image signal is alternatively applied between the common electrode
and the pixel electrodes to which the image signal having the second potential is
supplied and between the common electrode and the pixel electrodes to which the image
signal having the first potential is supplied.
[0011] Accordingly, it is possible to surely move the electrophoretic particles between
the common electrode and the pixel electrodes. That is, one of each white particle
charged to the negative polarity and each black particle charged to the positive polarity
is surely moved toward the pixel electrode in the dispersion medium and the other
thereof is surely moved toward to the common electrode in the dispersion medium.
[0012] In particular, since in the image signal supply period, the voltage according to
the image signal corresponding to the image data associated with the same frame image
is applied repeatedly several times between the common electrode and the pixel electrodes
in a unit of the frame period, it is possible to surely attract the electrophoretic
particles toward the common electrode and the pixel electrodes while preventing the
electrophoretic particles from sinking and rising due to the convection currents of
the dispersion medium and the gravity action. Accordingly, it is possible to improve
the contrast of an image to be displayed.
[0013] As a result, in the electrophoretic display device according to the aspect of the
invention, it is possible to display a high-quality clear image while reducing a residual
image or irregularity in color or brightness between pixels, for example.
[0014] In the electrophoretic display device according to the aspect of the invention, the
third potential may be lower than the first potential and the fourth potential may
be higher than the second potential.
[0015] According to the aspect of the invention, the electrophoretic particles can be surely
moved toward the electrodes to be moved between the pixel electrodes and the common
electrode.
[0016] For example, when the first potential and the second potential are set to 15 V and
0 V, respectively, the third potential and the fourth potential may be set to 14.5
V and 0.5 V, respectively. A difference between the first potential and the third
potential and a difference between the second potential and the fourth potential may
be set as small as possible within ranges in which the first potential is not lower
than the third potential and the second potential is not higher than the fourth potential
even due to the image signal variation in the common potential.
[0017] The electrophoretic display device according to the aspect of the invention may further
include: on the first substrate, data lines and scanning lines which intersect one
another; transistors which are formed in correspondence to intersection of the data
lines and the scanning lines and electrically connected to the pixel electrodes; and
retention capacitors which are electrically connected between the transistors and
the pixel electrodes and temporarily hold the image signal. In addition, the image
signal supply unit supplies the image signal to the pixel electrodes through the data
lines and the scanning lines.
[0018] According to the electrophoretic display device, active matrix driving is possible.
Here, the image signal in the pixel electrode is maintained only for some time by
the retention capacitors temporarily holding the image signal supplied through the
data lines and the transistors. Accordingly, it is possible to further improve the
contrast of an image to be displayed.
[0019] According to another aspect of the invention, there is provided a method of driving
an electrophoretic display device including a pair of first and second substrates,
an electrophoretic element which is interposed between the first and second substrates
and includes a dispersion medium containing electrophoretic particles, a plurality
of pixel electrodes which are formed on the first substrate, a common electrode which
is formed opposite the plurality of pixel electrodes on the second substrate, an image
signal supply unit which supplies an image signal having a first potential or a second
potential lower than the first potential to the plurality of pixel electrodes in accordance
with image data, and a common potential supply unit which supplies a common potential
to the common electrode. The method includes: supplying the image signal to the plurality
of pixel electrodes in accordance with image data associated with the same frame image
as the image data in each of a predetermined number of frame periods in an image signal
supply period containing the predetermined number of frame periods by the image signal
supply unit; and switching the common potential into a third potential equal to or
lower than the first potential and higher than the second potential and a fourth potential
lower than the third potential and equal to or higher than the second potential, and
supplying the switched potentials to the common electrode in each of the frame periods
in the image signal supply period by the common potential supply unit.
[0020] According to the method of driving the electrophoretic display device according to
the another aspect of the invention, like the electrophoretic display device described
above, it is possible to surely move the electrophoretic particles between the common
electrode and the pixel electrodes. Moreover, it is possible to surely attract the
electrophoretic particles toward the common electrode and the pixel electrodes while
preventing the electrophoretic particles from sinking and rising due to the convection
currents of the dispersion medium and the gravity action. As a result, the high-quality
image can be displayed.
[0021] Even in the method of driving the electrophoretic display device according to another
aspect of the invention, the electrophoretic display device described above according
to the aspect of invention can be adopted.
[0022] According to still another aspect of the invention, there is provided an electronic
apparatus including the electrophoretic display device having the above-described
configuration.
[0023] Since the electronic apparatus includes the electrophoretic display device described
above, it is possible to realize various electronic apparatus such as a wrist watch,
an electronic paper, an electronic note, a cellular phone, a portable audio apparatus
capable of displaying a high-quality image.
[0024] Operations and other advantages of the invention are apparent from exemplary embodiments
described below.
[0025] Embodiments of the invention will now be described by way of example only with reference
to the accompanying drawings, wherein like numbers reference like elements, and in
which:
[0026] Fig. 1 is a block diagram illustrating an overall configuration of an electrophoretic
display device according to a first embodiment.
[0027] Fig. 2 is an equivalent circuit diagram illustrating an electric configuration of
pixels of the electrophoretic display device according to the first embodiment.
[0028] Fig. 3 is a partial sectional view illustrating a display unit of the electrophoretic
display device according to the first embodiment.
[0029] Fig. 4 is a schematic diagram illustrating the configuration of a micro capsule.
[0030] Fig. 5 is a timing chart illustrating a method of driving the electrophoretic display
device according to the first embodiment.
[0031] Fig. 6 is a timing chart illustrating the method of driving the electrophoretic display
device according to the first embodiment.
[0032] Figs. 7A to 7D are schematic diagrams illustrating the states of electrophoretic
particles when the electrophoretic display device is driven according to the first
embodiment.
[0033] Fig. 8 is timing chart illustrating a modified example of Fig. 5.
[0034] Fig. 9 is a perspective view illustrating the configuration of an electronic paper
which is an example of an electronic apparatus using the electrophoretic display device.
[0035] Fig. 10 is a perspective view illustrating the configuration of an electronic book
which is an example of the electronic apparatus using the electrophoretic display
device.
[0036] Hereinafter, preferred embodiments of the invention will be described with reference
to the drawings.
First Embodiment
[0037] An electrophoretic display device will be described with reference to Figs. 1 to
Fig. 6 and Figs. 7A to 7D according to a first embodiment.
[0038] First, an overall configuration of the electrophoretic display device will be described
with reference to Figs. 1 to 2 according to this embodiment.
[0039] Fig. 1 is a block diagram illustrating the overall configuration of the electrophoretic
display device according to this embodiment.
[0040] According to this embodiment, as shown in Fig. 1, an electrophoretic display device
1 includes a display unit 3, a controller 10, a scanning line driving circuit 60,
a data line driving circuit 70, and a common potential supply circuit 220.
[0041] In the display unit 3, pixels 20 arranged in m rows by n columns are formed in a
matrix shape (two-dimensional surface). In addition, m scanning lines 40 (that is,
scanning lines Y1, Y2, ..., and Ym) and n data lines 50 (that is, data lines X1, X2,
..., and Xn) intersect each other in the display unit 3. Specifically, the m scanning
lines 40 extend in a row direction (that is, an X direction) and the n data lines
50 extend in a column direction (that is, a Y direction). The pixels 20 are disposed
in correspondence to locations where the m scanning lines 40 and the n data lines
50 intersect each other.
[0042] The controller 10 controls operations of the scanning line driving circuit 60, the
data line driving circuit 70, and the common potential supply circuit 220. For example,
the controller 10 supplies a clock signal and a timing signal such as a start pulse
to the circuits. In addition, the controller 10 may be included in or be an example
of "an image signal supply unit" related to the invention in addition to the scanning
line driving circuit 60 and the data line driving circuit 70 described below and may
constitute "a common potential supply unit" related to the invention in addition to
or instead of the common potential supply circuit 220 described below.
[0043] The scanning line driving circuit 60 supplies a pulse scanning signal sequentially
to the scanning lines Y1, Y2, ..., and Ym on the timing signal supplied from the controller
10.
[0044] The data line driving circuit 70 supplies an image signal to the data lines X1, X2,
..., and Xn on the basis of the timing signal supplied from the controller 10. The
image signal takes a binary potential of a high potential VH (for example, 15 V) or
a low potential VL (for example, 0 V). In this embodiment, the image signal having
the low potential VL is supplied to the pixels 20 to be displayed with a black color
and the image signal having the high potential VH is supplied to the pixels 20 to
be displayed with a white color.
[0045] In this embodiment, in a reset period before an image signal supply period in which
the image signal is supplied to the pixels 20, the scanning line driving circuit 60
supplies the high potential VH to all the m scanning lines 40 and the data line driving
circuit 70 supplies the low potential VL to all the n data lines 50, as described
below.
[0046] The common potential supply circuit 220 supplies a common potential Vcom to common
potential lines 93.
[0047] Various signals are input to and output from the controller 10, the scanning line
driving circuit 60, the data line driving circuit 70, and the common potential supply
circuit 220, but signals which are not related to this embodiment will not be described.
[0048] Fig. 2 is an equivalent circuit diagram illustrating an electric configuration of
the pixels.
[0049] In Fig. 2, each of the pixels 20 includes a pixel switching transistor 24, a pixel
electrode 21, a common electrode 22, an electrophoretic element 23, and a retention
capacitor 27.
[0050] The pixel switching transistor 24 is formed of an N-type transistor, for example.
In the pixel switching transistor 24, a gate is electrically connected to the scanning
line 40, a source is electrically connected to the data line 50, and a drain is electrically
connected to the pixel electrode 21 and the retention capacitor 27. The pixel switching
transistor 24 outputs the image signal supplied from the data line driving circuit
70 (see Fig. 1) through the data line 50 to the pixel electrode 21 and the retention
capacitor 27 at timing according to a pulse scanning signal supplied from the scanning
line driving circuit 60 through the scanning line 40 (see Fig. 1).
[0051] The image signal is supplied from the data line driving circuit 70 to the pixel electrodes
21 through the data lines 50 and the pixel switching transistors 24. The pixel electrodes
21 are disposed opposite the common electrode 22 with the electrophoretic element
23 interposed therebetween.
[0052] The common electrode 22 is electrically connected to the common potential lines 93
to which the common potential Vcom is supplied.
[0053] The electrophoretic element 23 includes a plurality of micro capsules which each
contain the electrophoretic particles.
[0054] The retention capacitor 27 is constituted by a pair of electrodes disposed opposite
to each other through a dielectric film. One electrode of the retention capacitor
27 is electrically connected to the pixel electrode 21 and the pixel switching transistor
24 and the other electrode thereof is electrically connected to the common potential
line 93. The retention capacitor 27 holds the image signal for some time.
[0055] Next, a detailed configuration of the display unit of the electrophoretic display
device will be described with reference to Figs. 3 and 4 according to this embodiment.
[0056] Fig. 3 is a partial sectional view illustrating the display unit of the electrophoretic
display device according to this embodiment.
[0057] In Fig. 3, the display unit 3 has a configuration in which the electrophoretic element
23 is interposed between an element substrate 28 and a counter substrate 29. This
embodiment will be described on the assumption that an image is displayed on a side
of the counter substrate 29. The element substrate 28 is an example of "a first substrate"
according to the invention and the counter substrate 29 is an example of "a second
substrate" according to the invention.
[0058] The element substrate 28 is formed of glass or plastic, for example. On the element
substrate 28, even through not shown, a laminated structure is formed in which the
pixel switching transistors 24, the retention capacitors 27, the scanning lines 40,
the data lines 50, the common potential lines 93, and the like described above with
reference to Fig. 2 are laminated. On upper side of the laminated structure, the plurality
of pixel electrodes 21 are arranged in a matrix shape.
[0059] The counter substrate 29 is a transparent substrate formed of glass or plastic, for
example. The common electrode 22 in a solid state is formed opposite the plurality
of pixel electrodes 9a on the plane of the counter substrate 29 opposite the element
substrate 28. The common electrode 22 is formed of a transparent conductive material
such as silver magnesium (MgAg), indium tin oxide (ITO), indium zinc oxide (IZO).
[0060] The electrophoretic element 23 includes the plurality of micro capsules 80 containing
the electrophoretic particles. The electrophoretic element 23 is fixed between the
element substrate 28 and the counter substrate 29 by a binder 30 formed of a resin
or the like and an adhesive layer 31. In the electrophoretic display device 1 according
to this embodiment, an electrophoretic sheet formed by fixing the electrophoretic
element 23 to the counter substrate 29 by the binder 30 in advance is attached to
the separately manufactured element substrate 28 provided with the pixel electrodes
21 by the adhesive layer 31.
[0061] The micro capsules 80 are interposed between the pixel electrodes 21 and the common
electrode 22. In addition, one or the plurality of micro capsules 80 are disposed
within one pixel 20 (in other words, for one pixel electrode 21).
[0062] Fig. 4 is a schematic diagram illustrating the configuration of the micro capsule.
The cross section of the micro capsule is schematically shown in Fig. 4.
[0063] In Fig. 4, the micro capsule 80 includes a dispersion medium 81, a plurality of white
particles 82, and a plurality of black particles 83 within a coat membrane 85. The
micro capsule 80 has a spherical shape with a particle diameter of about 50 µm, for
example. The white particles 82 and the black particles 83 are examples of "electrophoretic
particles" of the invention.
[0064] The coat membrane 85 functions as an outer shell of the micro capsule 80 formed of
transparent polymer resin such as acryl resin such as polymethyl methacrylate and
polyethyl methacrylate, urea resin, gum Arabic, and gelatine.
[0065] The dispersion medium 81 is a medium for dispersing the white particles 82 and the
black particles 83 in the micro capsule 80 (in the words, the coat membrane 85). Examples
of the dispersion medium 81 include water, alcoholic solvent (such as methanol, ethanol,
isopropanol, butanol, octanol, and methyl cellosolve), esters (such as ethyl acetate
and butyl acetate), ketones (such as acetone, methylethyl ketone, and methyl isobutyl
ketone), aliphatic hydrocarbons (such as pentane, hexane, and octane), alicyclic hydrocarbons
(such as cyclohexane and methyl cyclohexane), aromatic hydrocarbons (such as benzene,
toluene, and benzenes having a long-chain alkyl group (such as xylene, hexyl benzene,
heptyl benzene, octyl benzene, nonyl benzene, decyl benzene, undecyl benzene, dodecyl
benzene, tridecyl benzene, and tetradecyl benzene)), halogenated hydrocarbon (such
as methylene chloride, chloroform, carbon tetrachloride, and 1,2-dichloroethane),
carboxylate salt, and other oil substances. These materials may be used singly or
as a mixture. The dispersion medium 81 may be mixed with surfactant.
[0066] The white particles 82 are particles (polymer or colloid) formed of white pigments
such as titanium dioxide, zinc flower, and antimony trioxide and are charged to, for
example, negative polarity.
[0067] The black particles 83 are particles (polymer or colloid) formed of black pigments
such as aniline black and carbon black and are charged to, for example, positive polarity.
[0068] Accordingly, the white particles 82 and the black particles 83 move in the dispersion
medium 81 thanks to an electric field generated by a potential difference between
the pixel electrodes 21 and the common electrode 22.
[0069] A charging control agent including particles of electrolyte, surfactant, metal soap,
resin, rubber, oil, varnish, or compound, a dispersion solvent such as titanium coupling
agent, aluminum coupling agent, and silane coupling agent, lubricant, and stabilizer
may be added to the pigments as needed.
[0070] In Figs. 3 and 4, when voltage is applied between the pixel electrodes 21 and the
common electrode 22 so that the potential of the common electrode 22 is relatively
higher, the black particles 83 charged to the positive polarity are attracted toward
the pixel electrodes 21 within the micro capsules 80 by the Coulomb force and the
white particles 82 charged to the negative polarity are attracted toward the common
electrode 22 within the micro capsules 80 by the Coulomb force. As a result, the white
particles 82 are gathered on a side of a display surface (that is, a side of the common
electrode 22) within the micro capsules 80 to display a color (that is, a white color)
of the white particles 82 on the display surface of the display unit 3. Conversely,
when voltage is applied between the pixel electrodes 21 and the common electrode 22
so that the potential of the pixel electrodes 21 is relatively higher, the white particles
82 charged to the negative polarity are attracted toward the pixel electrodes 21 by
the Coulomb force and the black particles 83 charged to the positive polarity are
attracted toward the common electrode 22 by the Coulomb force. As a result, the black
particles 83 are gathered on a side of the display surface within the micro capsules
80 to display a color (that is, a black color) of the black particles 83 on the display
surface of the display unit 3.
[0071] Red, green, and blue colors can be displayed by replacing the pigments used for the
white particles 82 and the black particles 83 with pigments of the red, green and
blue colors, for example.
[0072] Next, a method of driving the electrophoretic display device according to this embodiment
will be described with reference to Figs. 5 to 7. Hereinafter, among the plurality
of pixel electrodes 21 arranged in the display unit 3, the pixel electrodes 21 of
the pixels 20 to be displayed with the black color are referred to as pixel electrodes
21 B and the pixel electrodes 21 of the pixels 20 to be displayed with the white color
are referred to as pixel electrodes 21W.
[0073] Figs. 5 and 6 are timing charts illustrating the method of driving the electrophoretic
display device according to this embodiment. In Fig. 5, time-dependent variation in
the common potential Vcom, the potentials of the scanning lines Y1, Y2, ..., and Ym,
and the potentials of the data lines X1, x2, ..., and Xn in an imaging period is shown
(that is, a period in which a new image is prepared or written to the plurality of
pixels 20 arranged in the display unit 3). In Fig. 6, time-dependent variation in
the potential of the common electrode 22, the potential of the pixel electrodes 21
B, the potential of the pixel electrodes 21 W in the imaging period is shown. Figs.
7A to 7D are schematic diagrams illustrating the states of the electrophoretic particles
upon driving the electrophoretic display device according to this embodiment. Fig.
7A shows the state of the electrophoretic particles immediately after a reset period.
Fig. 7B shows the state of the electrophoretic particles immediately after a first
frame period. Fig. 7C shows the state of the electrophoretic particles immediately
after a second frame period. Fig. 7D shows the state of the electrophoretic particles
immediately after the imaging period.
[0074] As shown in Fig. 5, a reset operation of displaying the white color on the display
surface of the display unit 3 in a reset period RT before an image signal supply period
(which is a period in which the image signal is supplied to the pixels 20) in the
imaging period is first performed.
[0075] That is, as shown in Figs. 5 and 6, in the reset period RT, the scanning line driving
circuit 60 (see Fig. 1) supplies the high potential VH to all the m scanning lines
40 (that is, the scanning lines Y1, Y2, ..., and Ym) and the data line driving circuit
70 supplies the low potential VL to all the n data lines 50 (that is, the data lines
X1, X2, ..., and Xm). In this way, the low potential VL supplied to the data lines
50 is supplied to the pixel electrodes 21 of the pixels 20 via the pixel switching
transistors 24 which are turned ON by the high potential VH supplied through the scanning
lines 40. Accordingly, in the reset period RT, the pixel electrodes 21 (all the pixel
electrodes 21 B and the pixel electrodes 21 W) of the pixels 20 are maintained in
the low potential VL (see Fig. 6). On the other hand, in the reset period RT, the
common potential supply circuit 220 (see Fig. 1) supplies the high potential VH as
the common potential Vcom to the common potential lines 93. Accordingly, in the reset
period RT, the common electrode 22 is maintained in the high potential VH (see Fig.
6).
[0076] As shown in Fig. 7A, in the reset period RT, the black particles 83 charged to the
positive polarity are attracted toward the pixel electrodes 21 in the dispersion medium
81 by the Coulomb force and the white particles 82 charged to the negative polarity
are attracted toward the common electrode 22 in the dispersion medium 81 by the Coulomb
force. As a result, the white color is displayed on the display surface of the display
unit 3.
[0077] As shown in Fig. 5, the image signal is supplied to the pixels 20 in the image signal
supply period followed after the reset period RT in the imaging period. In this embodiment,
the image signal supply period is set as a period which is L (where L is a natural
number of 2 or more) times of the frame period or a vertical scanning period (that
is, which is set in advance as a period for supplying the scanning signal sequentially
to all the m scanning lines 40). The image signal supply period contains a first frame
period FT(1), a second frame period FT(2), ..., and an L frame period FT(L) in this
order. In addition, each of the frame periods may be set to be in the range of 10
ms to 400 ms, for example.
[0078] Specifically, in the first frame period FT(1) in the image signal supply period,
the scanning line driving circuit 60 sequentially supplies the pulse scanning signal
to the scanning lines Y1, Y2, ..., and Ym in every horizontal scanning period, and
the data line driving circuit 70 supplies the image signal having the high potential
VH (for example, 15 V) or the low potential VL (for example, 0 V) to the data lines
X1, X2, ..., and Xn at timing according to the scanning signal. In the example shown
in Fig. 5, in the first frame period FT(1), the image signal having the high potential
VH is supplied to the data lines X1 and Xn and the image signal having the low potential
VL is also supplied to the data line X2 (in other words, the data line X2 is constantly
maintained in the low potential VL) in the initial horizontal scanning period at timing
at which the pulse scanning signal is supplied to the scanning line Y1; the image
signal having the high potential VH is supplied to the data lines X2 and Xn and the
image signal having the low potential VL is also supplied to the data line X1 in the
next horizontal scanning period at timing at which the pulse scanning signal is supplied
to the scanning line Y2; and the image signal having the high potential VH is supplied
to the data line X2 and the image signal having the low potential VL is also supplied
to the data lines X1 and Xn in an m-th horizontal scanning period at timing at which
the pulse scanning signal is supplied to the scanning line Ym. That is, in accordance
with an image to be displayed, the image signal having the high potential VH is supplied
to the pixel electrodes 21 B of the pixel 20 to be displayed with the black color
and the image signal having the low potential VL is also supplied to the pixel electrodes
21W of the pixels 20 to be displayed with the white color.
[0079] As shown in Fig. 6, the pixel electrodes 21 B are constantly maintained in the high
potential VH thanks to the potential held by the retention capacitors 27 until the
supply of the next image signal having the high potential VH at least in the second
frame period FT(2) described below, when the image signal having the high potential
VH is supplied at the timing at which the pulse scanning signal is supplied to the
scanning lines 40.
[0080] On the other hand, as shown in Figs. 5 and 6, the common potential supply circuit
220 (see Fig. 1) supplies the low potential VL as the common potential Vcom to the
common potential lines 93 in the first frame period FT(1). Accordingly, in the first
frame period FT(1), the common electrode 22 is constantly maintained in the low potential
VL (see Fig. 6).
[0081] As shown in Fig. 7B, in the first frame period FT(1), the black particles 83 charged
to the positive polarity are attracted toward to the common electrode 22 in the dispersion
medium 81 by the Coulomb force and the white particles 82 charged to the negative
polarity are attracted toward the pixel electrodes 21 B in the dispersion medium 81
by the Coulomb force between the common electrode 22 constantly maintained in the
low potential VL and the pixel electrodes 21 B constantly maintained in the high potential
VH. On the other hand, in the first frame period FT(1) neither the white particles
82 nor the black particles 83 are acted by the Coulomb force, since there is no potential
difference between the common electrode 22 constantly maintained in the low potential
VL and the pixel electrodes 21 W constantly maintained in the high potential VL.
[0082] Next, as shown in Fig. 5, in the second period FT(2) followed after the first frame
period FT(1), the scanning line driving circuit 60 sequentially supplies the pulse
scanning signal to the scanning lines Y1, Y2, ..., and Ym in every horizontal scanning
period, and the data line driving circuit 70 supplies the image signal having the
high potential VH or the low potential VL to the data lines X1, X2, ..., and Xn at
timing according to the scanning signal. In this embodiment, the data line driving
circuit 70 supplies the image signal associated with an image to be equally displayed
in each of the first frame period FT(1), the second frame period FT(2), ..., and the
L frame period FT(L) in the image signal supply period. Accordingly, in the second
frame period FT(2), the same image signal as the image signal in the first frame period
FT(1) is supplied. That is, in the second frame period FT(2), the same image signal
as the image signal in the first frame period FT(1) is written to the pixel electrodes
21 and the retention capacitors 27.
[0083] As shown in Fig. 6, in the second frame period FT(2), the pixel electrodes 21 B are
constantly maintained in the high potential VH and the pixel electrodes 21 W are constantly
maintained in the low potential VL. In this embodiment, since the image signal associated
with the image to be equally displayed is supplied to the pixel electrodes 21 in each
of the first frame period FT(1), the second frame period FT(2), ..., and the L frame
period FT(L), the pixel electrodes 21 B are constantly maintained in the high potential
VH and the pixel electrodes 21 W are constantly maintained in the low potential VL
even in the third frame period FT(3), ..., and the L frame period FT(L).
[0084] On the other hand, as shown in Figs. 5 and 6, the common potential supply circuit
220 (see Fig. 1) supplies the high potential VH as the common potential Vcom to the
common potential lines 93 in the second frame period FT(2). Accordingly, the common
electrode 22 is constantly maintained in the high potential VH in the second frame
period FT(2) (see Fig. 6).
[0085] As shown in Fig. 7C, in the second frame period FT(2), in the pixel electrodes 21
B neither the white particles 82 nor the black particles 83 are acted by the Coulomb
force, since there is no potential difference between the common electrode 22 constantly
maintained in the high potential VH and the pixel electrodes 21 B constantly maintained
in the high potential VH. On the other hand, in the second frame period FT(2), between
the common electrode 22 constantly maintained in the high potential VH and the pixel
electrodes 21 W constantly maintained in the low potential VL, the white particles
82 charged to the negative polarity are attracted toward the common electrode 22 in
the dispersion medium 81 by the Coulomb force and the black particles 83 charged to
the positive polarity are attracted toward the pixel electrodes 21 W in the dispersion
medium 81 by the Coulomb force.
[0086] In Figs. 5 and 6, the driving in the first frame period FT(1) is also performed in
the third frame period FT(3) followed after the second frame period FT(2). Accordingly,
like the driving in the first frame period FT(1) described with reference to Fig.
7B, in the third frame period FT(3), between the common electrode 22 constantly maintained
in the low potential VL and the pixel electrodes 21 B constantly maintained in the
high potential VH, the black particles 83 charged to the positive polarity are attracted
toward the common electrode 22 by the Coulomb force and the white particles 82 charged
to the negative polarity are attracted toward to the pixel electrodes 21 B by the
Coulomb force. On the other hand, neither the white particles 82 nor the black particles
83 are acted by the Coulomb force between the common electrode 22 constantly maintained
in the low potential VL and the pixel electrodes 21 W constantly maintained in the
low potential VL.
[0087] The driving in the first frame period FT(1) is performed in the fifth frame period
FT(5), the seventh frame period FT(7), etc. (that is, odd-numbered frame periods from
an initial odd frame period in the image signal supply period).
[0088] In Figs. 5 and 6, the driving in the second frame period FT(2) is also performed
in the fourth frame period FT(4) followed after the third frame period FT(3). Accordingly,
like the driving in the second frame period FT(2) described above with reference to
Fig. 7C, in the fourth frame period FT(4), neither the white particles 82 nor the
black particles 83 are acted by the Coulomb force between the common electrode 22
constantly maintained in the high potential VH and the pixel electrodes 21 B constantly
maintained in the high potential VH. On the other hand, between the common electrode
22 constantly maintained in the high potential VH and the pixel electrodes 21 W constantly
maintained in the low potential VL, the white particles 82 charged to the negative
polarity are attracted toward the common electrode 22 by the Coulomb force and the
black particles 83 charged to the positive polarity are attracted toward the pixel
electrodes 21 W by the Coulomb force.
[0089] The driving in the second frame period FT(2) is also performed in the sixth frame
period FT(6), the eighth frame period FT(8), etc. (even-numbered frame periods from
an initial even frame period in the image signal supply period).
[0090] In this way, in the image signal supply period, the voltage according to the image
signal is repeatedly applied in an alternate manner between the common electrode 22
and the pixel electrodes 21 B and between the common electrode 22 and the pixel electrodes
21 W. That is, in the odd-numbered frame periods such as the first frame period FT(1)
and the third frame period FT(3), the voltage is applied between the common electrode
22 constantly maintained in the low potential VL and the pixel electrodes 21 B constantly
maintained in the high potential VH, and no voltage is applied between the common
electrode 22 constantly maintained in the low potential VL and the pixel electrodes
21 W constantly maintained in the low potential VL. On the other hand, in the even-numbered
frame periods such as the second frame period FT(2) and the fourth frame period FT(4),
no voltage is applied between the common electrode 22 constantly maintained in the
high potential VH and the pixel electrodes 21 B constantly maintained in the high
potential VH, and the voltage is applied between the common electrode 22 constantly
maintained in the high potential VH and the pixel electrodes 21 W constantly maintained
in the low potential VL.
[0091] Accordingly, in the image signal supply period, the white particles 82 and the black
particles 83 are surely moved between the common electrode 22 and the pixel electrodes
21. That is, it is possible to surely move one of each white particle 82 charged to
the negative polarity and each black particle 83 charged to the positive polarity
toward the pixel electrode 21 in the dispersion medium 81 and surely move the other
thereof toward the common electrode 22 in the dispersion medium 81.
[0092] In this embodiment, the voltage according to the same image signal is applied repeatedly
several times between the common electrode 22 and the pixel electrodes 21 in a unit
of the frame period in the image signal supply period. Therefore, it is possible to
surely attract the white particles 82 and the black particles 83 toward the common
electrode 22 and the pixel electrodes 21 while preventing the white particles 82 and
the black particles 83 from sinking and rising due to the convection currents of the
dispersion medium 81 and the gravity action. That is, the voltage according to the
same image signal is repeatedly applied between the common electrode 22 and the pixel
electrodes 21 B in the odd-numbered frame periods (the first frame period FT(1), the
third frame period FT(3), etc.) in the image signal supply period (see Fig. 7B). Moreover,
the voltage according to the same image signal is repeatedly applied between the common
electrode 22 and the pixel electrodes 21 W in the even-numbered frame periods (the
second frame period FT(2), the fourth frame period FT(4), etc.) in the image signal
supply period (see Fig. 7C). Accordingly, it is possible to surely attract the white
particles 82 and the black particles 83 toward the common electrode 22 and the pixel
electrodes 21 when the image signal supply period ends (that is, immediately after
the L frame period), as shown in Fig. 7D.
[0093] According to the electrophoretic display device 1 described in this embodiment, the
voltage according to the same image signal is applied repeatedly several times between
the common electrode 22 and the pixel electrodes 21 in a unit of the frame period
in the image signal supply period, even when a period holding the image signal is
relatively shorter in the pixel electrodes 21 and the retention capacitors 28 due
to a relatively small capacitance value of the retention capacitors 28. Accordingly,
it is possible to surely attract the white particles 82 and the black particles 83
toward the common electrode 22 and the pixel electrodes 21.
[0094] As a result, according to the electrophoretic display device 1 described in this
embodiment, it is possible to display a high-quality clear image while reducing irregularity
in color or brightness between pixels.
[0095] In Figs. 5 and 6, after the imaging period, the common electrode 22 and the pixel
electrodes 21 (in addition to the common potential lines 93, the scanning lines 40,
and the data lines 50) become a high-impedance state (Hi-Z), that is, an electrically
disconnected state. In this way, it is possible to prevent leak current between the
pixel electrodes 21 adjacent to each other from occurring. Moreover, by suppressing
power consumption, it is possible to surely hold the image signal in each of the pixels.
[0096] In this embodiment, the reset period RT is provided, but the reset period RT need
not be provided.
[0097] Fig. 8 is a timing chart illustrating a modified example of the driving method in
Fig. 5.
[0098] As the modified example, as shown in Fig. 8, the common potential Vcom is switched
into a high potential Va lower by a potential difference ΔV than the high potential
VH of the image signal and a low potential Vb higher by a potential difference ΔV
than the low potential VL of the image signal, and the high potential Va and the low
potential Vb are supplied to the common electrode 22. For example, when the high potential
VH and the low potential VL are 15 V and 0 V, respectively, the high voltage Va and
the low potential Vb are set to 14.5 V and 0.5 V (that is, the differential ΔV is
set to 0.5 V).
[0099] Even in this case, it is possible to surely move the white particles 82 and the black
particles 83 toward the pixel electrodes 21 and the common electrode 22.
[0100] In the odd-numbered frame periods (the first frame period FT(1), the third frame
period FT(3), etc.) in the image signal supply period, the potential of 0.5 V is added
to the common electrode 22. Therefore, even when the potential of the retention capacitors
28 is lowered, the white particles 82 charged to the negative polarity can be held
at the common electrode 22 thanks to the fact that the potential of the common electrode
22 is higher by 0.5 V than the pixel electrodes 21 W which is in the low potential
VL. Accordingly, it is possible to prevent the white particles 82 and the black particles
83 from migrating toward an opposite side (moving backward).
[0101] Likewise, in the even-numbered frame periods (the second frame period FT(2), the
fourth frame period FT(4), etc.) in the image signal supply period, the potential
of the common electrode 22 is lowered by 0.5 V from the high potential VH. Therefore,
even when the potential of the retention capacitors 28 is lowered, the black particles
83 charged to the positive polarity can be held at the common electrode 22 thanks
to the fact that the potential of the common electrode 22 is lower by 0.5 V than that
of the pixel electrodes 21 B which is in the high potential VH. Accordingly, it is
possible to prevent the white particles 82 and the black particles 83 from moving
backward.
Electronic Apparatus
[0102] Next, an electronic apparatus to which the electrophoretic display device described
above is applied will be described with reference to Figs. 9 and 10. Hereinafter,
examples in which the electrophoretic display device is applied to an electronic paper
and an electronic note will be described.
[0103] Fig. 9 is a perspective view illustrating the configuration of an electronic paper
1400.
[0104] As shown in Fig. 9, the electronic paper 1400 includes the electrophoretic display
device according to the above-described embodiment as a display unit 1401. The electronic
paper 1400 has a flexible property and includes a main body 1402 formed of a rewritable
sheet having texture like paper and flexibility.
[0105] Fig. 10 is a perspective view illustrating the configuration of an electronic note
1500.
[0106] As shown in Fig. 10, the electronic note 1500 has a configuration in which plural
sheets of electronic papers 1400 shown in Fig. 10 are bound and inserted into a cover
1501. The cover 1501 includes a display data input unit (not shown) for inputting
display data supplied from an external device. Accordingly, the display details can
be changed or updated on the basis of the display data with the bound electronic paper.
[0107] Since the electronic paper 1400 and the electronic note 1500 described above include
the electrophoretic display device according to the above-described embodiment, it
is possible to realize low power consumption and a high quality image display.
[0108] The electrophoretic display device according to the above-described embodiment can
be applied to a display unit of an electronic apparatus such as a wrist watch, a cellular
phone, or a portable audio apparatus in addition to the electronic paper and the electronic
note.
[0109] The invention is not limited to the above-described embodiment, but may be modified
in various forms without departing from the scope or idea of the invention understood
from the accompanying claims and the entire specification. A modified electrophoretic
display device, a method of driving the modified electrophoretic display device, and
an electronic apparatus including the modified electrophoretic display device are
included in the technical scope of the invention.